It is known that an immunoglobulin is schematically made up of two heavy chains and two light chains. Determinations of the presence of the free light chains, also called Bence Jones proteins, in the urine is of great interest from the diagnostic viewpoint.
The free light chains are present in traces in the serum of normal subjects but are practically absent in the urine. The presence of said light chains in the urine is an indication of the existence of a pathological condition, particularly of immunological nature.
Actually, the presence of free light chains in urine presupposes their anomalous increase in the serum of the subject but, given their low molecular weight, free light chains pass through the glomerular filter and do not persist in the blood. It is therefore necessary to perform an indirect investigation, ascertaining their presence in the urine.
The presence of free light chains in the urine, which is the consequence of the increase thereof in the blood, is associated with immunological pathologies which can be summarized as (a) the presence of monoclonal free light chains, i.e. immunoproliferative illnesses such as multiple myeloma, micromolecular myeloma, Waldenstrom's macroglobulinemia, chronic lymphatic leukemia and primitive amyloidosis; and (b) the presence of polyclonal free light chains, i.e. hyperimmune illnesses such as systemic lupus erythematosus, acute rheumatoid arthritis and secondary amyloidosis.
Diagnostic methods based on ascertainment of free light chains in the urine are of great interest but at present are blocked by the difficultes of performance of such an investigation. At present, the most widely used method calls for electrophoretic analysis of the concentrated urine.
This technique necessarily requires concentration of the sample because of the relatively small percentage of free light chains in the organic liquid even with serious pathological conditions of the subject. Electrophoretic examination of the unconcentrated sample results in unacceptably low sensitivity and the resulting unreliability. The time necessary for concentration is added however to the time required for electrophoretic analysis with the obvious drawbacks. The analysis performed on the concentrated samples undoubtedly raises the reliability of the results without however achieving reasonable certainty. On the samples which prove suspect under electrophoresis it is therefore very advisable to perform immunofixation or immunoelectrophoretic tests, the laboriousness and cost of which are known, to achieve truly satisfactory levels of sensitivity and hence reliability of the analysis results.